1. Technical Field of the Invention
The present invention relates in general to the mobile telecommunications field and, in particular, to a method and apparatus for controlling radio network resources in a cellular communications system.
2. Description of Related Art
Generally, the use of packet switching in mobile communications systems will provide operators with a versatile platform for a large variety of data applications. In fact, communications system developers anticipate that packet switched communications will form a significant part of the future's mobile telephony traffic. Consequently, it is important to ensure that future packet switched systems will be capable of operating effectively in a wide range of communications environments. It is also important to ensure that future packet switched systems will be developed with a high degree of network design flexibility.
In existing packet switched mobile systems, control over the radio network (e.g. air interface) is exercised by control logic (e.g., software algorithms) executed in processors located in the mobile stations. In contrast, radio network control in most circuit switched mobile systems is exercised by control logic at the network, which sends dedicated control messages to specified mobile stations. The primary reason for mobile station radio network control in a packet switched system is to avoid incurring the substantial signalling load that would result from the network signalling simultaneously to a multitude of packet mode mobile stations waiting in the standby mode.
On the other hand, centralized radio network control (from the network side) provides an operator with wider, more comprehensive and efficient control over the network. As such, more sophisticated control algorithms can be employed by the network control entity, and the control data can be processed in a much more efficient manner than in decentralized networks where mobile stations exercise the radio network control.
An important advantage of centralized radio network control is that higher quality traffic connections can be made, which in turn, leads to higher network capacities. This benefit is the primary reason that centralized radio network control is used in circuit switched systems operating in the active mode. However, such a benefit currently cannot be obtained for packet switched systems operating in the ready (or active) mode, because the majority of packet switched data transfers occur during relatively short periods of time. Specifically, in contrast to circuit switched connection durations, packet data transmissions are generally too short in duration to leave adequate time for optimization adjustments in the radio network (e.g., individual handovers, power level adjustments, etc.).
If a packet switched system and circuit switched system share a frequency band in the same geographical area, growth in each system's mobile station population contributes to increased radio signal interference with the other's traffic. In such a multi-service environment, the packet switched system is typically an add-on to an existing circuit switched system having a relatively large subscriber base. Consequently, the amount of packet switched traffic being carried is relatively small compared to the circuit switched traffic. Therefore, it follows that a higher percentage of packet switched traffic than circuit switched traffic will be subject to signal interference. This interference occurs primarily because the cell borders for the packet switched traffic and the cell borders for the circuit switched traffic differ from each other due to differences between the cell selection algorithms for the two types of traffic.
In existing cellular communications systems, control over the radio network is exercised either by a network entity (or entities) or the mobile stations. In other words, no existing cellular system operator has the option of determining which of the two (network or mobiles) shall exercise overall radio network control. Specifically, the important radio network functions of cell selection and re-selection, and mobile stations' power calculations are controlled either by the network entity or the mobile stations involved. For example, in the Nordic Mobile Telephone (NMT) System, Total Access Communications System (TACS), Advanced Mobile Phone System (AMPS), Digital Advanced Mobile Phone System (D-AMPS), Global System for Mobile Communications (GSM), Personal Digital Cellular (PDC) System, and IS-95 Code Division Multiple Access (CDMA) System, one or more network entities exercise control over the radio network in the active mode, while the mobile stations exercise control over the radio network in the idle mode. On the other hand, in the Digital European Cordless Telephone (DECT) circuit switched system and the Cellular Digital Packet Data (CDPD) and Mobitex packet switched systems, the mobile stations exercise control over the radio network in both the active and idle modes. In other words, it is the mobile stations that exercise control over the radio network in the idle mode, in all of the above-named systems.